We discuss the linear and nonlinear rheology of concentrated silicone oil-in-water emulsions, amorphous disordered solids composed of repulsive and deformable soft colloidal spheres. Based on recent results from simulation and theory, we derive quantitative predictions for the dependences of the elastic shear modulus and the yield stress on the effective droplet volume fraction [1]. The remarkable agreement with experiments we observe supports the scenario that the repulsive glass and the jammed state can be clearly identified in the rheology of soft spheres at finite temperature while crossing continuously from a liquid to a highly compressed yet disordered solid. For emulsions of nanoscale droplets, known as nanoemulsions, however, the radius begins to approach the Debye screening length and these systems can become elastic solids at very low droplet volume fractions, even as low as about twenty percent. For this case the concept of an effective volume fraction cannot properly account for the electrostatic repulsions. To address the rheology of nanoemulsions we combine the interaction potential associated with droplet jamming and deformation with a full treatment of the screened charge repulsion between charged droplets [2]. Finally we show that the onset of elasticity due to entropic contribution can be described by a quasi-equilibrium analytical model of linear elasticity that includes energetic contributions from entropy and soft interfacial deformation [3]. The comparison of the comprehensive, yet simple, models with experimental data demonstrates the possibility to describe the rheology of a wide range of charge-stabilized emulsions having droplet sizes ranging from the macroscale to the nanoscale.
[1] F. Scheffold, F. Cardinaux and T. G. Mason, J. Phys.: Condens. Matter 25, 502101 (2013), IOP Select
[2] F. Scheffold, J. N. Wilking, J. Haberko, F. Cardinaux,and T. G. Mason, submitted
[3] T. G. Mason and F. Scheffold, submitted
frank.scheffold@unifr.ch
